<!DOCTYPE html>
<html lang="zh_CN">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

</body>
<script type="text/javascript">

    function sum(a, b) {

        console.log(a + b);

        /* 函数如果没有返回值，系统内部默认返回 undefined */
        // return undefined;

    }


    var a = 12;
    var b = 24;


    console.log(sum(a, b)); // 函数如果没有返回值，系统内部默认返回 undefined
    var rs = sum(a, b);
    console.log(rs);


</script>

</html>
